Unmount your external media card; if they are not already mounted you don't have to do this

umount /media/mmc1
umount /media/mmc2

Install the n810 install tools. You cannot access the internal or external memory card in this process, otherwise you'll get an error from the clone package. Installing the package will repartition and formatsyour SD card and will ERASE all the data on it, so be careful when doing it. This process also clones the maemo system on the flash onto the SD card. When run successfully.

dpkg -i install-tools-N810e.deb

If this process fails, it is probably because you didn't umount your external media. The medial is unmounted during this process so just try installing the install tools again.

Reboot the n810

Install KDE4

During the boot up, hold the memory key (lower left on the drawer keyboard, right under the direction pad) and you'll get a boot menu. Choose the third option (External MMC card) to boot from SD, the first one will boot from flash.

Install KDE4. This should pull in all the necessary dependencies (75MB of packages) as well. I had to force install kdebase-workspace to start plasma on the device. You can do that from a remote ssh session with su user and setting the display export DISPLAY=:0.

apt-get install kdebase-workspace kdebase-runtime kdeplasma-addons

If that all works, you can replace the hildon desktop with plasma. At the moment it crashes and reboots the n810, so you might not want to do this.